Ruthenium Isotope Composition of Allende Refractory Metal Nuggets

Abstract

Refractory metal nuggets (RMNs) are among the first solids formed in the nascent solar system. They contain high abundances of refractory metals like Re, Os, W, Ir, Ru, and Pt. The isotopic compositions of these elements bear testimony to the stellar sources that contributed to the nucleosynthetic makeup of our solar system. We report the first high-precision Ru isotope data for a bulk RMN sample prepared from the Allende meteorite. The RMNs display well-resolved mass-independent anomalies with positive anomalies for 96 Ru, 98 Ru, 100 Ru, 102 Ru, and 104 Ru. These are best explained by a deficit in r -process combined with a slight deficit in p -process nuclides. This finding stands in stark contrast to the s -process deficit isotopic patterns observed for Allende Ca–Al-rich inclusions (CAIs), bulk Allende, and other bulk meteorites. The contrasting r -, p -deficit versus s -deficit Ru isotopic signatures observed between RMNs and CAIs is surprising, given that CAIs are assumed to be a major host phase of RMNs. One way to explain the s -deficit patterns observed for CAIs and bulk meteorites is that r - and p -process Ru nuclides were added to the solar nebula after RMN formation and prior to the formation of CAIs and the accretion of meteorite parent bodies. A possible source may have been a nearby core-collapse supernova that injected freshly synthesized r - and p -process nuclides into the nascent solar system. The injection of such r - and p -enriched matter represents an alternative mechanism to account for the s -process variability presented by CAIs and bulk carbonaceous meteorites.